postgresql - PostgreSQL - 别名列和 HAVING

Question

SELECT  
CASE WHEN SUM(X.Count)*3600 is null THEN  '0'  
            ELSE  
            SUM(X.Count)*3600  
       END AS PJZ,  
       X.Mass  
FROM X  
WHERE X.Mass > 2000  
HAVING ((X.Mass / PJZ * 100) - 100) >= 10;

获取：错误：列 »pjz« 不存在。

我怎么能做这样的事情？

Answer 1

您不能在有中使用别名，并且必须在有子句中复制该语句。由于您只想检查 null，您可以这样做：

SELECT coalesce(SUM(X.Count)*3600, 0) AS PJZ, X.Mass
FROM X
WHERE X.Mass > 2000
HAVING ((X.Mass / coalesce(SUM(X.Count)*3600, 0) * 100) - 100) >= 10; 

Answer 2

将其包装到派生表中：

SELECT CASE 
          WHEN PJZ = 0 THEN 100
          ELSE PJZ
       END as PJZ,
       mass
FROM (
    SELECT CASE 
             WHEN SUM(X.Count)*3600 is null THEN '0'  
             ELSE SUM(X.Count)*3600  
           END AS PJZ,  
           X.Mass  
    FROM X  
    WHERE X.Mass > 2000  
    GROUP BY X.mass
) t
WHERE PJZ = 0 
   OR ((X.Mass / PJZ * 100) - 100) >= 10;

（请注意，我添加了缺少的组，否则查询将无效）

Answer 3

其他选项是通过WITH语句包围查询 - 例如：

WITH x as (
  SELECT coalesce(SUM(X.Count)*3600, 0) AS PJZ, X.Mass
  FROM X
  WHERE X.Mass > 2000
)
SELECT * from X WHERE PJZ >=10

在我看来，这比代码重复要好得多